Stents are used not only as a mechanical intervention in vascular conditions but also as a vehicle for providing biological therapy. As a mechanical intervention, stents act as scaffoldings, functioning to physically hold open and, if desired, to expand the wall of the passageway. Typically, stents are capable of being compressed, so that they can be inserted through small vessels via catheters, and then expanded to a larger diameter once they are at the desired location. Examples in patent literature disclosing stents that have been applied in PTCA procedures include stents illustrated in U.S. Pat. No. 4,733,665 issued to Palmaz, U.S. Pat. No. 4,800,882 issued to Gianturco, and U.S. Pat. No. 4,886,062 issued to Wiktor.
Biological therapy can be achieved by medicating the stents. Medicated stents provide for the local administration of a therapeutic substance at the diseased site. In order to provide an efficacious concentration to the treated site, systemic administration of such medication often produces adverse or toxic side effects on the patient. Local delivery is a preferred method of treatment in that smaller total levels of medication are administered in comparison to systemic dosages, but are concentrated at a specific site. Local delivery thus produces fewer side effects and achieves more favorable results.
In many patients, especially diabetic patients, stentable lesions are focal manifestations of widespread vascular disease. The advent of drug delivery stents has brought relief from restenosis of the treated lesion, but leaves progression of regional vascular disease unaddressed.
Nitric oxide (NO) has numerous physiologic and pathophysiologic functions. For example, NO can inhibit the inflammatory process by lowering cytokine synthesis and inactivating nuclear factor (NF)-κB,3 as several cytokines contain a binding site for NF-κB in their promoter regions. It has been reported that blood level NO can inhibit platelet adhesion and aggregation, inflammation, and smooth muscle cell migration and proliferation and can stimulate endothelial cell migration and proliferation. In addition, NO has vasorelaxant effect and can regulate smooth muscle contractility and platelet reactivity (see, e.g., Lindberg, L., et al., Nitric Oxide gives maximal response after coronary artery bypass surgery. J. Cardiothorac Vasc. Anesth. 8:182-87 (1994)).
Therefore, the present invention provides means of generating nitric oxide to cure the deficiencies of a conventional drug delivery stent.